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Unravelling the mystery of ice ages using ancient molecules

It seems there was ‘a distinct increase in sea ice extent’ at some point in time that led to a switch to longer ice age intervals, but the reason(s) for it are not known.

Researchers from Cardiff University have revealed how sea ice has been contributing to the waxing and waning of ice sheets over the last million years, says Phys.org.

In a new study published in the journal Nature Communications, the team have shown for the first time that ice ages, occurring every 100,000 years, are accompanied by a rapid build-up of sea ice in the Earth’s oceans.

Our planet’s ice ages used to occur at intervals of every 40,000 years, which made sense to scientists as the Earth’s seasons vary in a predictable way, with colder summers occurring at these intervals. However there was a point, about a million years ago, called the ‘Mid-Pleistocene transition’, in which the ice age intervals changed from every 40,000 years to every 100,000 years.

The reason why ice ages occur at these timescales has been a mystery to scientists for a long time.

By tracking molecules produced by tiny marine algae preserved in ocean sediments, the team have been able to reconstruct sea-ice conditions during the Mid-Pleistocene transition.

Their results showed that at the same time as the cycles of ice ages changed from 40,000 years to 100,000 years there was a distinct increase in sea ice extent and a change in the rhythm of sea ice build-up across climate cycles.

“Prior to the Mid-Pleistocene transition, sea ice build-up and decay during ice ages was more gradual, whereas in the late Pleistocene, when the cyclicity of ice ages changed, we observed conditions characterised by a prominent short-lived peak in sea ice extent during late ice ages,” said Henrieka Detlef, a postgraduate researcher at Cardiff University School of Earth and Ocean Sciences who led the study.

With less water evaporating into the atmosphere, there would be less moisture being transported to continental glaciers which, in turn, would cause them to retreat and help in the transition from an ice age to a warm period.

“It’s clear that sea ice plays a fundamental role in the transition from an ice age into a warm stage every 100,000 years,” Detlef continued.

“Understanding the interactions of sea ice with the regional ecosystem and oceanography is particularly important with respect to anthropogenic climate change and a rapidly shrinking sea ice cover in the Arctic Ocean. Our study is an important step forward in understanding the role of sea ice for long-term climate change.”

The quote was: “Prior to the Mid-Pleistocene transition, sea ice build-up and decay during ice ages was more gradual, whereas in the late Pleistocene, when the cyclicity of ice ages changed, we observed conditions characterised by a prominent short-lived peak in sea ice extent during late ice ages”

Maybe the key phrase there is ‘whereas in the late Pleistocene’? Some of the variations do get bigger.

This doesn’t compute with mid-Pleistocene, but movement of plates/continents/ocean blockages that permitted the Antarctic Ocean to go freewheeling and swirling around its southern continent seems destined to significantly change glacials and interglacials. When that cold ocean water had to be mixed with the warmer, I imagine things were very different. Is there anything to this idea from the experts?

Thanks, Roger and other contributors for always informative and engaging posts and articles and comments. Very much appreciated.

pyromancer76 ‘s piece ” –movement of plates/continents/ocean blockages–” are the ‘collateral damage’ but not the main causative. Which is obliquity. But all are tethered to a faulty theory re obliquity.

The Earth’s thermostat is basically provided by the interplay between gravity and the unique properties of water via the atmospheric Rankine Cycle. This mechanism is very good at keeping the Earth cool in the event of excess radiation. However it is not good at warming things up and could be said to be counterproductive here due to the high Albedo of ice, snow and clouds. Hence I suspect the reason why we experience long periods of very cold conditions as ice ages.

What puzzles me is how the Earth subsequently warms up once an ice age has been generated. My pure guess is that it is the energy which gets trapped in the core which eventually warms the oceans and then melts the sea ice. But this takes a long time; but enabled because the Rankine Cycle gets slowed down due to lack of humidity.

The system described in that paper is mechanism that might have changes the earth’s obliquity. It is exactly what was found in archaeological research, except it does not take millennia, but a couple of centuries at certain points in time. Nothing definite, but it is the nearest mechanism that explains the evidence. The evidence says that it is not only obliquity that changes abruptly but also the earth’s crust which effects ocean currents.

Oldmark: Thanks for that. Have looked at your two links and cannot but agree with respect to the very long term situation. all the factors mentioned having their influences.

However I was mainly considering the present situation prevailing hopefully for the next century or so. And it is here that I invoke the part played by water and its relationship with gravity both of which have constants embedded whereby these constants effectively control the global temperature but within limits as you rightly point out. In fact a very effective thermostat as of now.

We could get embroiled in the detailed thermodynamics of this; but I suspect you are well aware of this, so won’t pursue it.

All I can say is that as long as my kettle always boils at 100 C I will be content that planet Earth will not be overheating, however worry a bit if things start cooling and my heating bills escalate.

As for the current politicised panic – That is another matter and I despair.

Archaeology says the next flip is to a low tilt. Dynamics, if I interpret correctly, indicate that if Iz << Ix,Iy (melted ice caps) the tendency for a more vertical rotation would exist. Last change was over 4k yrs away, and if the next may not be due in another 4k (and I'm over seventy) I won't worry.

But as stated at top, the greatest dangers are likely of our own creation.